A microprocessor-controlled, automated extraction/concentration device, the Prep 1 (Du Pont Clinical Systems), was evaluated for application to the isolation of drug substances from postmortem fluids and tissue homogenates. Two classes of materials were investigated: barbiturates and the benzodiazepine, diazepam. With as little as 200 mg of tissue, barbiturate derivatives were successfully isolated and measured by gas chromatography using nitrogen-phosphorus detection with a coefficient of variation of 2 to 5%. Diazepam was measured in a similar fashion with a coefficient of variation of 4.4%. Preliminary investigation indicates that this system is applicable to a wide range of drug substances of toxicological interest.